In recent years, xenon is often used as flash light sources at a macro inspection in producing semiconductors or light-emitting gases of a plasma display. On the other hand, only an extremely trace amount of xenon is contained in the air. Accordingly, in a method of separating and producing xenon from air, it is necessary to take in a large amount of air and refine xenon by undergoing complicated separating/refining processes. Accordingly, xenon of high purity is very expensive, and it is very important to establish a system to recover, refine and reuse used xenon.
For example, moisture and carbon dioxide are removed from xenon in a detector of an X-ray inspection apparatus with a zeolite adsorbing layer. Thereafter, other impurity gases are removed with a getter layer. A method of refining and recovering xenon in this manner is proposed (e.g., see PTL 1).
Also, first, moisture is adsorbed and removed from liquid oxygen containing xenon and krypton by silica gel or the like. Thereafter, a Li- or Ag-exchanged X zeolite is used for an adsorbent to selectively adsorb xenon at low temperature. A method of recovering xenon by desorbing xenon from the zeolite is proposed (e.g., see PTL 2).
Further, as a method of removing impurities contained in effluent gases of various steps using rare gases such as xenon efficiently, there is proposed a method of efficiently separating and removing a trace of impurities such as hydrogen, water vapor and nitrogen oxide from a mixed gas predominantly composed of a rare gas and a nitrogen gas (e.g., see PTL 3 and PTL 4).
Moreover, as a method of functionally excluding moisture, carbon dioxide and the like from effluent gases emitted in a semiconductor production process to recover a high purity of xenon gas, there is proposed a method in which impurities are removed by zeolite or a separation membrane module, and then xenon is adsorbed on a zeolite having a pore diameter of 5 angstroms or more under pressures to be recovered (see PTL 5).
Moreover, in order to make an effective use of emitted xenon containing a trace of radioactive krypton, a refining technology, using a PSA (Pressure Swing Absorption) purge method, of recovered xenon is proposed (see Non-PTL 1). In the refining technology of recovered xenon, xenon is adsorbed from the mixed gas of xenon and krypton under pressures by use of a Na—X zeolite or a Ca—X zeolite as the adsorbent to selectively adsorb xenon.
Currently, equipment in which xenon is enclosed (e.g. plasma display, semiconductor production apparatus) is disposed of, and then is disassembled/separated/recovered at a disposal field for recycle or buried in a landfill. However, xenon is released to the atmosphere during disassembly and is little recovered.
Xenon released to the atmosphere is controlled so as to be below an air standard concentration. However, atmospheric release of xenon is not preferred since disassembling workers may inhale a trace of xenon. Therefore, it is desirable that in a step of disassembling equipment or steps up to burying equipment in a landfill, xenon can be adsorbed from the inside of the equipment under ordinary temperatures and pressure or under ordinary temperatures and low xenon partial pressures without special environments or introduction of facilities. Moreover, a technology capable of recovering the adsorbed xenon is necessary.
However, in the constitutions described in PTLs 1 to 5 and Non-PTL 1, xenon is recovered by removing impurities from xenon gases including impurities, which are emitted from a plant or the like, or by a method in which an adsorbent adsorbs xenon under pressures or at low temperature. Therefore, it is difficult to recover xenon directly from the used equipment in which xenon is enclosed with efficiency under ordinary temperatures and pressure or under ordinary temperatures and low xenon partial pressures.